The present invention relates to apparatus which have a keyboard for inputting information/commands to the device, and more particularly, to the prevention of a user from inputting incompatible information/commands during power-up of the apparatus.
Scanned matrix keyboards are almost universally employed in control system which include microcontrollers, due to the efficiency of scanned matrix keyboards in minimizing the number of wire connections required. In a scanned matrix keyboard, a set of drive lines and a set of sense lines are logically organized as rows and columns, and each of a plurality of individual key switches is electrically positioned at the intersection between a particular drive line and a particular sense line to electrically and logically connect a particular sense line to a particular drive line to define a matrix intersection point when the switch is actuated by a user.
Thus a coding pattern is established from an encoding set including connection of a sense line to at least a particular one of the set of drive lines according to the programming of the microprocessor. Conventional practice is to periodically scan the keyboard, e.g., by momentarily applying a bias or signal to each of the drive lines in sequence, while monitoring all of the sense lines in synchronism with the activation of the drive lines, and thereby determining which particular key is being actuated.
With television receivers/players, e.g., color television receiver, VCR, DVD players, if a user by chance happens to press a particular combination of keyboard keys while powering-up the device, the receiver may switch into an undesirable service mode, which is intended to be used only during factory production set-up procedures. Once the television receiver is switched into such a service mode, the user is very confused, and is unable to use the keys to switch out from the service mode, i.e., the user does not know that he/she must disconnect the AC power cord from the AC power, and should wait until capacitors within the television receiver discharge before re-inserting the AC plug. It is desirable to avoid this situation from occurring.
A control system for an apparatus wherein a keyboard for information or command input has a plurality of drive lines and a plurality of sense lines coupled to a programmable microprocessor. The keyboard includes a plurality of switch elements arranged to selectively connect a particular one of the plurality of drive lines to a particular one of the set of sense lines. The programming of the microprocessor disables the control system during power-up to prevent incompatible user input during initialization.